First Results from the TNG50 Simulation: Galactic outflows driven by supernovae and black hole feedback (1902.05554v2)

Abstract: We present the new TNG50 cosmological, magnetohydrodynamical simulation -- the third and final volume of the IllustrisTNG project. This simulation occupies a unique combination of large volume and high resolution, with a 50 Mpc box sampled by 2160^3 gas cells (baryon mass of 8x10^4 Msun). The median spatial resolution of star-forming ISM gas is ~100-140 parsecs. This resolution approaches or exceeds that of modern 'zoom' simulations of individual massive galaxies, while the volume contains ~20,000 resolved galaxies with M*>10^7 Msun. Herein we show first results from TNG50, focusing on galactic outflows driven by supernovae as well as supermassive black hole feedback. We find that the outflow mass loading is a non-monotonic function of galaxy stellar mass, turning over and rising rapidly above 10^10.5 Msun due to the action of the central black hole. Outflow velocity increases with stellar mass, and at fixed mass is faster at higher redshift. The TNG model can produce high velocity, multi-phase outflows which include cool, dense components. These outflows reach speeds in excess of 3000 km/s out to 20 kpc with an ejective, BH-driven origin. Critically, we show how the relative simplicity of model inputs (and scalings) at the injection scale produces complex behavior at galactic and halo scales. For example, despite isotropic wind launching, outflows exhibit natural collimation and an emergent bipolarity. Furthermore, galaxies above the star-forming main sequence drive faster outflows, although this correlation inverts at high mass with the onset of quenching, whereby low luminosity, slowly accreting, massive black holes drive the strongest outflows.

• The paper presents first results from the high-resolution TNG50 simulation, examining galactic outflows driven by supernova and black hole feedback.
• Key findings include a non-monotonic mass loading factor depending on stellar mass and increasing outflow velocities with stellar mass and redshift.
• Despite simple model inputs, the simulation naturally shows complex, multiphase outflows with emergent collimation and high-velocity components.

Overview of the TNG50 Simulation Study

The paper "First Results from the TNG50 Simulation: Galactic outflows driven by supernovae and black hole feedback" by Nelson et al. presents a detailed examination of galactic outflows based on the cosmological magnetohydrodynamical simulation TNG50, a part of the IllustrisTNG project. This work explores the dynamics driven by supernovae and black hole (BH) feedback, highlighting the intricate interplay between stellar and supermassive black hole-driven processes in galaxy formation and evolution.

Key Findings

1. Resolution and Volume:
   • TNG50 achieves a unique combination of high resolution and large volume, with a 50 Mpc box sampled by $2160^3$ gas cells. It features a baryon mass resolution of $8 \times 10^4$ and a median spatial resolution of star-forming interstellar medium (ISM) gas of 100-140 parsecs.
2. Mass Loading and Outflow Velocities:
   • The paper finds that the mass loading factor, which is the ratio of the mass outflow rate to the star formation rate (SFR), is non-monotonic with galaxy stellar mass. The mass loading decreases with increasing stellar mass up to $10^{10.5}$ solar masses, then rises due to the influence of supermassive black holes, highlighting a transition from supernova-driven to BH-driven winds.
   • Outflow velocities are found to increase with stellar mass and are faster at higher redshifts.
3. Complex Outflow Behaviors:
   • The outflows exhibit complex behaviors at galactic and halo scales from relatively simple model inputs. A notable observation is the natural collimation and emergent bipolarity of outflows despite isotropic wind launching.
   • Multiphase outflows include high-velocity components with speeds exceeding 3000 km/s at distances up to 20 kpc, indicating the significant role of BH-driven feedback.
4. Dependence on Galactic Properties:
   • There is a correlation between outflow velocity and the galaxy's position relative to the star-forming main sequence (SFMS). Galaxies above the SFMS drive faster outflows, though this trend inverts at high mass due to quenching, where slowly accreting BHs drive the strongest outflows.

Implications and Future Directions

The TNG50 results provide critical insights into the mechanisms of galaxy formation and evolution. The natural emergence of complex outflows from relatively straightforward feedback models underscores the importance of such simulations in understanding galaxy dynamics.

• Practical Implications:
  • Understanding the detailed processes driving outflows can help refine models of galaxy evolution and feedback processes in simulations.
  • These insights are also valuable for interpreting observations of outflows and their impact on galaxy properties and evolutionary trajectories.
• Theoretical Implications:
  • The paper's findings can inform theoretical models of gas dynamics and feedback, emphasizing the need to account for the emergent behavior of outflows at various scales.
  • Detailed comparisons with observational data will be crucial to validate these models and enhance the understanding of the baryon cycle in and around galaxies.

Future studies could focus on directly comparing these simulations with observed outflows, refining the physical models, and using TNG50 to explore other aspects of galaxy formation, such as interaction with the circumgalactic medium and the role of magnetic fields. These efforts will be pivotal in advancing the field of computational astrophysics and enhancing interpretations of cosmic structure formation.